The present invention relates to homokinetic joints and in particular such joints which allow a wide angular deviation between the two joint parts and comprise an axial retaining device.
The homokinetic joints of the invention are adapted to interconnect two shafts or like members and comprise a first element in the shape of a tulip rigid with one of the two shafts to be connected and defining raceways and a second element rigid with the other shaft and comprising a hub from which extend the trunnions on which are rotatably and slidably mounted rollers received in the raceways of the first element. In a tripod joint the tulip-shaped element defines three raceways having a part-circular section and each receiving a roller carried by each of the three trunnions of the second element which consequently has the shape of a tripod.
Such joints allow a wide angular deviation between the joint parts and are often axially fixed by providing between the tulip-shaped element and the hub of the element carrying the trunnions an axial retaining device allowing, on one hand, a ball joint movement and, on the other hand, a sliding movement in a direction perpendicular to the axis of one of the two shafts. For this purpose, the tulip element is usually at least partly closed by a resiliently yieldable attachment comprising a plurality of branches which are hooked onto corresponding branches of the tulip element, this attachment defining in its centre part a retaining surface for the hub of the element defining the trunnions. There is also provided at least one thrust member which is slidably mounted in the hub of the tripod element along the axis of the associated shaft. This member usually has the shape of a mushroom which has a stem received in the hub and comprises a radial shoulder capable of coming in contact with a radial bearing surface of the hub.
It has been found that in certain applications, and in particular in front-drive vehicles, such joints are subjected to vibrations produced by the vehicle driving engine unit, the state of the road and various frictions. The axial retaining system is then stressed cyclically and to obtain a silent and durable operation, two conditions must be satisfied, namely:
1. A given prestressing force must be exerted in the axial retaining device.
2. The axial rigidity of this retaining device must be as high as possible in order to avoid that it be put into resonance under the effect of the cyclic excitations coming mainly from the engine.
Now, these two conditions are practically impossible to satisfy simultaneously since the prestressing force to be exerted depends to a large extent on the algebraic sum of the manufacturing tolerances of the various component parts of the joint and in particular the tulip element, the resiliently yieldable attachment, the hub of the tripod element and the mushroom-shaped thrust member. Moreover, the clipping of the resiliently yieldable attachment can only be achieved under axial prestress since this clipping occurs when the joint is already in the assembled position and therefore under unfavourable conditions of access and visibility.